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Homework Help: Rain and man on incline

  1. Jun 19, 2015 #1
    1. The problem statement, all variables and given/known data
    Rain falls with velocity of 20m/s parallel to an incline which is at an angle of 37 degrees from the ground. A man starts running down the incline with a velocity 'v' . Find 'v' such that the rain appears to be falling vertically on the man( from his perspective).

    2. Relevant equations

    3. The attempt at a solution
    I am confused about the axis i must take. Should i take the x axis on the horizontal of the incline or the ground? I suppose i must resolve the rain into it's rectangular components. But using what angle? Please help.
  2. jcsd
  3. Jun 19, 2015 #2
    If you really want to understand this problem, I suggest using the ground (not the ramp) as the x-axis, draw a vector for the rain, and draw vector for the man running, make each vector a part of a right triangle and break them into components via trigonometry. This is the long way to solve the problem, but it will give you insight into any future problems like this that you encounter.

    Keep in mind that you want the man and the rain in the same horizontal frame of reference, so the rain is only moving relative to the man in the vertical frame of reference.
  4. Jun 20, 2015 #3


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    The question isn't making sense to me. Is this the exact wording? The rain is falling parallel to the slope?
  5. Jun 22, 2015 #4
    Not sure but I think like the followin':
  6. Jun 22, 2015 #5
    Dont know why the pic is not uploading

    Okay, let me tell like this:
    tan90=(20sin37/(v-20cos37)) so, v-20cos37=0
    Or, v=20cos37=15.9727

    Using relative motion
  7. Jun 22, 2015 #6


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    We are still waiting for the original poster to tell us what the question is. Posting answers seems premature.
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